Field of the Invention and Related Statement
The present invention relates to a ceramic turbo charger rotor having a ball bearing structure, particularly to a ceramic turbo charger rotor in which an angular ball bearing and a spacer are assembled to an outer surface of a journal shaft of the ceramic turbo charger rotor as one unit.
The ceramic turbo charger rotor in which a ceramic turbine rotor and a metal compressor rotor are connected by a metal shaft is generally used by being assembled to a bearing housing which is supported by a floating metal or a ball bearing.
The balance of such ceramic turbo charger rotor is corrected in such a manner that the unbalance of the ceramic turbine rotor is firstly corrected when the metal shaft is assembled to the ceramic turbine rotor, and then the balance of the turbo charger rotor as a whole is corrected when the metal compressor rotor is assembled to the metal shaft by means of a nut.
FIG. 1 is a schematic view showing a ceramic turbo charger rotor having a ball bearing structure. The ceramic turbo charger rotor 11 comprises a ceramic turbine rotor 12 and a metal shaft 13 comprising a journal shaft 13a, and an inner race 14 and a spacer 15 assembled to an outer surface of the journal shaft 13a as one unit. Hitherto, two ways have been suggested for assembling the spacer 15 to connecting portions 13b and 13c of the journal shaft 13a: pressure inserting and clearance fitting. When the spacer 15 is assembled to the connecting portions 13b and 13c of the journal shaft 13a by a pressure inserting manner, the balance of the turbo charger rotor 11 is corrected after the inner race 14 and the spacer 15 have been assembled to the journal shaft 13, as shown in FIG. 1. On the other hand, when the spacer 15 is assembled to the connecting portions 13b and 13c of the journal shaft 13 by a clearance fitting manner, the balance of the rotor 11 is corrected before assembling the inner race 14 and the spacer 15 to the journal shaft 13.
However, when the spacer 15 is assembled to the journal shaft 13 by a pressure inserting manner, a deviation between a center axis and a rotation axis of the ceramic turbo charger rotor occurs, and therefore the amount of unbalance of the ceramic turbo charger rotor is apt to become large due to the deviation. Thus a lot of working time is necessary to correct the unbalance of the ceramic turbo charge rotor, and the balance of the ceramic turbo charger rotor to which the metal compressor rotor has been assembled cannot be maintained under the influence of the deviation.
further, when the pacer 15 is assembled to the journal shaft 13 by a clearance fitting manner, precise processing and inspecting are required to provide a clearance in the spacer 15, because the clearance between the journal shaft 13 and the spacer 15 should be processed to about several .mu.m or less.